The DSP tab contains several groups of controls. The top centre group in the
DSP tab is for WBIR, or Wide Band Image Rejection. Any
signal images will be seen as identical 'mirror image' signals always symmetrically positioned either side of the display centre. These
will appear on all bands and as a signal tunes one way, the image will tune the other. If it does not look like that, it is not an image.
Even without WBIR, some image rejection should be obtained if the input audio channels have been balanced (see Sound Card).
Signals + Images
NB: If you do not have your audio levels fairly equal, or a mono signal, or the plugs/sockets make intermittent contact, you will have
images whatever you do. If you have not set the input level as described earlier (see Sound Card), the image rejection algorithm may
operate in less than optimum manner.
Because the only 'band' seen by NaP3 is the rig IF there is only one pair of correction values ever needed. They are always saved between
sessions. The pictures below enable options to optimise and/or lock these values into place.
Startup default Manually set
Seeding Auto
The first picture shows the setup default Manual setting with correction values of zero, and no image cancellation taking place.
'Old school' users may opt to remain in Manual, with the enabled Gain and Phase dropdowns offering the process of setting them manually.
Each of the values can be positive or negative and the DSP latency (processing delay) will cause the effect of any change to lag, especially
when getting close to the fine changes for optimum cancellation. These values will be true only for the image position in the display used to set
them, but may suffice much of the time across the display.
It is possible to speed up the process of acquiring values by Seeding with an S9+ signal, where an algorithm builds up values over about five
seconds, the values visible in the greyed out dropdowns. The S9+ signal can be from a generator or a single strong signal in a band, at least
30dB (5 S points) larger than any other in the band. When finished, WBIR will return to its previous setting with a new set of values. This can
be carried out at any time unless the signal is too too large, when a warning will appear. The values in the greyed-out dropdowns should
change fast at first and then slow as they converge on a good solution. If they dance about too much there are too many changing signals in the
band.
Engagaing the WBIR Auto algorithm will use the seeded values to constantly improve upon them to cancel any image in the display.With
Auto the optimum solution is found for the distribution of signals within the band at any time (this is left running in the author's setup).
UNDER NO CIRCUMSTANCES ATTEMPT TO CANCEL IMAGES WITH YOUR SOUND CARD BALANCE CONTROLS. WBIR
compensates for small amplitude imbalances between channels and you will wind up 'chasing your tail' with poor image cancellation.